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21.
On spin description of water-biopolymer interactions: theory and experiment of reentrant order-disorder transition.
Artem V. Badasyan, invited lecture at foreign university

Abstract: The experimental studies of biopolymer conformations have reached an unprecedented level of detailization during the past decade and allow now to study single molecules in vivo [1]. Processing of experimental data essentially relies on theoretical approaches to conformational transitions in biopolymers [2]. However, the models that are currently used, originate from the early 1960's and contain several unjustified assumptions, widely accepted at that time. Thus, the view on the conformational transitions in the polypeptides as a two-state process has very limited applicability because the all-or-none transition mechanism takes place only in short polypeptides with sizes comparable to the spatial correlation length; the original formulation of Zimm-Bragg model is phenomenological and does not allow for a microscopic model for water; the implicit consideration of the water-polypeptide interactions through the ansatz about the quadratic dependence of free energy difference on temperature can only be justified through the assumption of an ideal gas with a constant heat capacity. To get rid of these deficiencies, we augment the Hamiltonian formulation [3] of the Zimm-Bragg model [4] with the term describing the water-polypeptide interactions [5]. The analytical solution of the model results in a formula, ready to be fit to Circular Dichroism (CD) data for both heat and cold denaturation. On the example of several sets of experimental data we show, that our formula results in a significantly better fit, as compared to the existing approaches. Moreover, the application of our procedure allows to compare the strengths of inter- and intra-molecular H-bonds, an information, inaccessible before.
Found in: osebi
Keywords: helix-coil transition, water-polypeptide interactions
Published: 13.03.2019; Views: 632; Downloads: 0
.pdf Fulltext (78,48 KB)

22.
Perehod spiral'-klubok v kol'cevyh zamkiutyh DNK
Artem V. Badasyan, 2002, master's thesis

Found in: osebi
Published: 20.03.2019; Views: 708; Downloads: 0
.pdf Fulltext (137,83 KB)

23.
OMPC model' i uporjadočenija biopolimerov
Lusine Arutjunjan, 2019, master's thesis

Found in: osebi
Published: 30.05.2019; Views: 560; Downloads: 0
.pdf Fulltext (2,24 MB)

24.
DNA-CNT Physisorption
Artem V. Badasyan, invited lecture at foreign university

Found in: osebi
Keywords: DNA, CNT, zipper model, physisorption
Published: 28.01.2020; Views: 206; Downloads: 0
.pdf Fulltext (416,43 KB)

25.
Statistical mechanics of DNA-nanotube adsorption
Sh. A. Tonoyan, Davit Khechoyan, Yevgeni S. Mamasakhlisov, Artem V. Badasyan, 2019, other component parts

Abstract: Attraction between the polycyclic aromatic surface elements of carbon nanotubes (CNT) and the aromatic nucleotides of deoxyribonucleic acid (DNA) leads to reversible adsorption (physisorption) between the two, a phenomenon related to hybridization. We propose a Hamiltonian formulation for the zipper model that accounts for the DNA-CNT interactions and allows for the processing of experimental data, which has awaited an available theory for a decade.
Found in: osebi
Keywords: DNA-CNT physisorption, zipper model
Published: 28.01.2020; Views: 241; Downloads: 0
.pdf Fulltext (515,48 KB)

26.
27.
Statistical mechanics of DNA adsorption on a carbon nanotube
Sh. A. Tonoyan, Davit Khechoyan, Yevgeni S. Mamasakhlisov, Artem V. Badasyan, 2020, published scientific conference contribution abstract

Abstract: The attraction between the polycyclic aromatic surface elements of carbon nanotubes (CNT) and the aro- matic nucleotides of deoxyribonucleic acid (DNA) leads to reversible adsorption (physisorption) between them. With the goal to provide the theoretical support to numerous technologies on the basis of DNA-CNT hybrids, we propose a Hamiltonian formulation for the zipper model that accounts for relevant interactions and allows for the processing of experimental data, which has awaited an available theory for a decade.
Found in: osebi
Keywords: DNA, CNT
Published: 22.05.2020; Views: 108; Downloads: 7
.pdf Fulltext (2,96 MB)

28.
Statistical mechanics of DNA-nanotube adsorption
Artem V. Badasyan, Yevgeni S. Mamasakhlisov, Davit Khechoyan, Sh. A. Tonoyan, 2020, original scientific article

Abstract: Attraction between the polycyclic aromatic surface elements of carbon nanotubes (CNTs) and the aromaticnucleotides of deoxyribonucleic acid (DNA) leads to reversible adsorption (physisorption) between the two, aphenomenon related to hybridization. We propose a Hamiltonian formulation for the zipper model that accountsfor the DNA-CNT interactions and allows for the processing of experimental data, which has awaited an availabletheory for a decade.
Found in: osebi
Keywords: Carbon nanotubes, desoxyribonucleic acid, physisorption
Published: 30.06.2020; Views: 76; Downloads: 0
.pdf Fulltext (1,21 MB)

29.
Water reveals non-Arrhenius kinetics in protein folding experiments
Artem V. Badasyan, 2020, published scientific conference contribution abstract (invited lecture)

Abstract: Statistical theories describe systems in equilibrium, and cannot be used to study kinetics. However, the theo- ries are based on coarse-grained parameters, that include assumptions regarding the underlying kinetics. If such assumptions are incorrect, the theoretical expressions, used to process the experimental data, will not fit. I report on one such case we have met within the application of Zimm-Bragg [1] theory to process folding experiments, and discuss the reasons and consequences. Studies of relaxation phenomena in glass-forming liquids by default account for the shift in temperature by some value, corresponding to the glass formation temperature, .In particular, temperature shift appears in hydrated proteins because of the presence of partially glassy states giving rise to non- Arrhenius relaxation times log τ ~ [2]. A phenomenological approach was suggested by Adam and Gibbs as early as in 1965 to describe the sudden increase of viscosity and the slowing down of the collective modes in super-cooled liquids as the temperature is approaching[3]. The key idea of Adam-Gibbs theory was to consider the supercooled liquid as a set of clusters (cooperatively rearranging regions) of different sizes that change with temperature, giving rise to the shift in re- laxation time. The temperature shift factor is present in many theories describing properties of water. Thus, Truskett and Dill had to include the Adamm-Gibbs temperature shift into their simple analytical model of water to achieve the agreement with experimental data on the tem- perature dependence of self-diffusion coefficient [4]. Later, Schiro and Weik have summarised recent in vitro and in silico experimental results regarding the role of hydration water in the onset of protein structural dy- namics, and have reported the presence of super-Arrhenius relaxation region above the ”protein dynamic transition” temperature [4]. Recently, Mallamace et al have used the Adam-Gibbs theory in their NMR meas- urements of protein folding-unfolding in water [4] and to rationalise the complicated pressure-temperature diagrams in these glass-forming systems. Motivated by the considerations above, and taking into account the relationship between the unimolecular rate of folding in water and the relaxation time 45 , we introduce the tem- perature shift into the formulas used to fit experimental data on hydrated polypeptides. By doing so we resolve the paradox and complete the new method of processing the Circular Dichroism ex- perimental data on protein folding
Found in: osebi
Keywords: water, protein folding, non-Arrhenius kinetics
Published: 20.07.2020; Views: 28; Downloads: 3
.pdf Fulltext (2,35 MB)

30.
Entropic cost of folding and phase diagrams of polypeptides: Why are IDPs unfolded at room temperature?
Artem Badasyan, invited lecture at foreign university

Abstract: In spin models, that are applied to describe the conformational transitions in polymers, the number of spin orientations, that correspond to the disordered conformation, can be estimated using fundamental definitions of Statistical Physics. For instance, when considering alpha-helix to coil transition in polypeptides, the role of generalized coordinates is played by pairs of torsional angle, and the repeating unit populates different regions of that 2D contour map, depending on conformation. By scanning over all possible torsional angles, that do not violate the obvious limitations due to the excluded volume, the so-called Ramachandran map can be plotted, which is actually the phase space visualization for the helix-coil transition problem. The region of phase space, corresponding to the ordered, helical conformations, is much more limited, than the one, corresponding to all other (allowed) conformations. We can calculate the areas of these regions as Γhelix and Γcoil , and construct the ratio Q = Γcoil . Naturally, it can be interpreted as log(Q) = Scoil − Shelix = ΔS, the entropic cost of helix with respect to coil. To illustrate the importance of the entropic price of ordered conformation we report our recent results, that allowed to explain the peculiarity of phase diagrams of Intrinsically Disordered Proteins (IDP) out of larger Q-values, as compared to globular counterparts. In particular, it has been shown, that due to larger Q, the phase diagram of IDP is shifted towards higher temperatures.
Found in: osebi
Keywords: IDP, protein folding, phase diagram
Published: 23.06.2016; Views: 1874; Downloads: 0
.pdf Fulltext (2,96 MB)
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